A few weeks ago, Jay Stanley posted here about some of the dangers of “Big Data,” a sanitized term for data mining. When it’s employed by government security agencies in the search for terrorists, Jay wrote, there’s a substantial risk “that people will be tagged and suffer adverse consequences without due process, the ability to fight back, or even knowledge that they have been discriminated against.”

The government’s secret watch lists for suspected terrorists – including the No Fly List – provide a cautionary example. We don’t know what kind of “evidence” or innuendo is sufficient to land someone on the No Fly List, because the government won’t tell us. The FBI has created a “Frequently Asked Questions” page on its website, in which it explains that U.S. citizens may be placed on terrorist watch lists if “there is a reasonable suspicion that they are known or reasonably suspected of terrorism” – but that’s word soup, not a proper legal standard. What does it mean for the government to “suspect” that someone is “suspected of terrorism”? It means, in practice, that the government can place anyone on a watch list, on the basis of anything: an intercepted email, a suspicious association, a travel itinerary – or some algorithmic combination of all of those.

And once you’re on a watch list, you’re entirely at the government’s mercy if you want to get off. We’ve challenged this regime in federal court on behalf of fifteen U.S. citizens and legal residents who were not allowed to board flights but have never been given any explanation or opportunity to object. On Friday, my colleague Nusrat Choudhury appeared before the Ninth Circuit Court of Appeals to argue that placing our clients on the No Fly List without providing them any opportunity to confront and rebut the “evidence” against them is unconstitutional.

You can listen to the argument here. I’m always a little amazed when intelligent and collegial government lawyers stand up in court to defend the indefensible, but even by those standards, Friday’s hearing stood out. Chief Judge Alex Kozinski had a simple question for the government attorney: what would you do if you found yourself on the No Fly List? After some hemming and hawing, the attorney said that he would seek “redress” from the Department of Homeland Security – even though DHS does not place people on the No Fly list and has no authority to remove them (that’s the FBI’s job). Because, the lawyer conceded, DHS would not be able to confirm or deny whether he was on the list, he would then seek review in a federal appellate court. And what would the court be able to do?, asked Judge Kozinski. Not much, said the government lawyer. In fact, the lawyer would not even concede that a federal court possessed the authority to order someone removed from the No Fly List.

In other words, according to the United States government, the only redress that is available to a watch-listed citizen is to hope that some government bureaucrat will correct a mistake or change his mind. Judge Kozinski seemed frustrated by the government’s equivocation. “So many words,” he said during an earlier exchange. “So little meaning.”

The Due Process Clause of the Fifth Amendment doesn’t have very many words, but if those words are to retain their meaning, the Ninth Circuit will have to put a check on the government’s ability to blacklist its citizens without recourse.